Ciao a tutti, volevo aggiornare ubuntu all'ultima versione ma mi da questo errore

Si è verificato un problema durante l'aggiornamento. Solitamente si tratta di problemi di rete, controllare la connessione di rete e riprovare.


Failed to fetch http://ubuntu.fastbull.org/ubuntu/dists/feisty/Release Unable to find expected entry feisty/binary-i386/Packages in Meta-index file (malformed Release file?)

Failed to fetch http://ubuntu.fastbull.org/ubuntu/di...pdates/Release Unable to find expected entry feisty-security/binary-i386/Packages in Meta-index file (malformed Release file?)

Failed to fetch http://ubuntu.fastbull.org/ubuntu/di...curity/Release Unable to find expected entry feisty-security/binary-i386/Packages in Meta-index file (malformed Release file?)

Failed to fetch http://ubuntu.fastbull.org/ubuntu/di...oposed/Release Unable to find expected entry feisty-security/binary-i386/Packages in Meta-index file (malformed Release file?)

Failed to fetch http://ubuntu.fastbull.org/ubuntu/di...kports/Release Unable to find expected entry feisty-security/binary-i386/Packages in Meta-index file (malformed Release file?)

visto che la connessione di rete funziona cosa può essere? grazie in anticipo